<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 3//EN">
<HTML><HEAD>
		<TITLE>User's Guide - netCDF Files</TITLE>
		<META HTTP-EQUIV="keywords" CONTENT="GRAPHICS VISUALIZATION VISUAL PROGRAM DATA
MINING">
	<meta http-equiv="content-type" content="text/html;charset=ISO-8859-1">
</HEAD><BODY BGCOLOR="#FFFFFF" link="#00004b" vlink="#4b004b">
		<TABLE width=510 border=0 cellpadding=0 cellspacing=0>
			<TR>
				<TD><IMG SRC="../images/spacer.gif" WIDTH=80 HEIGHT=1></TD>
				<TD><IMG SRC="../images/spacer.gif" WIDTH=49 HEIGHT=1></TD>
				<TD><IMG SRC="../images/spacer.gif" WIDTH=24 HEIGHT=1></TD>
				<TD><IMG SRC="../images/spacer.gif" WIDTH=100 HEIGHT=1></TD>
				<TD><IMG SRC="../images/spacer.gif" WIDTH=3 HEIGHT=1></TD>
				<TD><IMG SRC="../images/spacer.gif" WIDTH=127 HEIGHT=1></TD>
				<TD><IMG SRC="../images/spacer.gif" WIDTH=6 HEIGHT=1></TD>
				<TD><IMG SRC="../images/spacer.gif" WIDTH=50 HEIGHT=1></TD>
				<TD><IMG SRC="../images/spacer.gif" WIDTH=71 HEIGHT=1></TD>
			</TR>
			<TR>
				<TD colspan=9><IMG src="../images/flcgh_01.gif" width=510 height=24 border="0" alt="OpenDX - Documentation"></TD>
			</TR>
			<TR>
				<TD colspan=2><A href="../allguide.htm"><IMG src="../images/flcgh_02.gif" width=129 height=25 border="0" alt="Full Contents"></A></TD>
				<TD colspan=3><A href="../qikguide.htm"><IMG src="../images/flcgh_03.gif" width=127 height=25 border="0" alt="QuickStart Guide"></A></TD>
				<TD><A href="../usrguide.htm"><B><IMG src="../images/flcgh_04d.gif" width=127 height=25 border="0" alt="User's Guide"></B></A></TD>
				<TD colspan=3><A href="../refguide.htm"><IMG src="../images/flcgh_05.gif" width=127 height=25 border="0" alt="User's Reference"></A></TD>
			</TR>
			<TR>
				<TD><A href="usrgu069.htm"><IMG src="../images/flcgh_06.gif" width=80 height=17 border="0" alt="Previous Page"></A></TD>
				<TD colspan=2><A href="usrgu071.htm"><IMG src="../images/flcgh_07.gif" width=73 height=17 border="0" alt="Next Page"></A></TD>
				<TD><A href="../usrguide.htm"><IMG src="../images/flcgh_08.gif" width=100 height=17 border="0" alt="Table of Contents"></A></TD>
				<TD colspan=3><A href="usrgu067.htm"><IMG src="../images/flcgh_09.gif" width=136 height=17 border="0" alt="Partial Table of Contents"></A></TD>
				<TD><A href="usrgu080.htm"><IMG src="../images/flcgh_10.gif" width=50 height=17 border="0" alt="Index"></A></TD>
				<TD><A href="../srchindx.htm"><IMG SRC="../images/flcgh_11.gif" width=71 height=17 border="0" alt="Search"></A></TD>
			</TR>
		</TABLE>
		<H2><A NAME="HDRNETCDF" ></A>B.4 netCDF Files</H2>
		<A NAME="IDX1021"></A><A NAME="IDX1022"></A>
<P>
Data Explorer supports the importation of data in netCDF format, a data
abstraction for self-describing multidimensional
Arrays.
It represents a simpler data model than that of Data Explorer, one similar to
that of the Array Object.
Data are accessed in netCDF through an application programming
interface (available in C and FORTRAN libraries from the
Unidata Program Center--in Boulder, Colorado).
<P>
Scalar data on a regular grid can be imported from a standard netCDF
file.
To import vector data, data on irregular grids, or time series data,
additional attributes must be added to the netCDF file.
These attributes allow you to specify the data, positions, and
connections components of your data set.
See <A HREF="usrgu071.htm#HDRAPE">B.5 , "netCDF Files: Complex Fields"</A> for
more information about these
attributes.
<P>
<H3><A NAME="Header_459" ></A>Regular Grids</H3>
<A NAME="IDX1023"></A>
<P>
To import scalar data on a regular grid, specify the netCDF file name
as the <TT><STRONG>name</STRONG></TT> parameter.
By default, all netCDF variables are imported and collected
into a Group.
To import one or more particular variables, specify their names as the
<TT><STRONG>variable</STRONG></TT> parameter.
The <TT><STRONG>format</STRONG></TT> parameter must be "netCDF."
<P>
Data Explorer automatically constructs positions and connections for each
variable, with an origin of 0.0 and spacings of 1.0 along each
dimension.
<P>
For data that is logically a vector Field, but whose values are stored
in three separate netCDF variables, each component of the vector
can be imported separately; the Compute module can then be
used to create a single vector Field.
<P>
For data that is logically a vector Field, but whose values are stored
as an <I>n</I>&#43;1 dimensional regular grid, use the Slice
and Compute modules to separate the components of the vector,
and then recombine them into a single vector Field.
<P>
<H4><U>Example of a Regular Grid</U></H4>
<P>
The following file describes a 3 &times; 3 &times; 3 regular grid at
origin 0, 0, 0 with deltas of 1.0 along each axis.
<PRE>
netCDF volume &#123;
dimensions:
   nx = 3;
   ny = 3;
   nz = 3;
</PRE>
<PRE>
variables:
   float field&#95;data(nx, ny, nz);

data:
   field&#95;data =
        0, 0, 0
        0, 0, 0
        0, 5, 0
</PRE>
<PRE>
        0, 0, 5
        0, 0, 0
        0, 0, 0
</PRE>
<PRE>
        5, 0, 0
        0, 0, 0
        0, 0, 0;
&#125;
</PRE>
<P>
netCDF on completely regular grids can be imported directly by
Data Explorer without modifying the netCDF file.
See <A HREF="#HDRNETCDF">B.4 , "netCDF Files"</A>
for more information.

		<P>
		<HR>
		<DIV align="center">
			<P><A href="../allguide.htm"><IMG src="../images/foot-fc.gif" width="94" height="18" border="0" alt="Full Contents"></A> <A href="../qikguide.htm"><IMG src="../images/foot-qs.gif" width="94" height="18" border="0" alt="QuickStart Guide"></A> <A href="../usrguide.htm"><IMG src="../images/foot-ug.gif" width="94" height="18" border="0" alt="User's Guide"></A> <A href="../refguide.htm"><IMG src="../images/foot-ur.gif" width="94" height="18" border="0" alt="User's Reference"></A></P>
		</DIV>
		<DIV align="center">
			<P><FONT size="-1">[ <A href="http://www.research.ibm.com/dx">OpenDX Home at IBM</A>&nbsp;|&nbsp;<A href="http://www.opendx.org/">OpenDX.org</A>&nbsp;] </FONT></P>
			<P></P>
		</DIV>
	</BODY></HTML>
